1. Technical Field
The present disclosure generally relates to light-emitting devices, and particularly to a light emitting diode (LED).
2. Description of Related Art
With developments in semiconductor technology, LEDs, which are new generation light-emitting devices, are widely used as backlight sources of the liquid crystal displays instead of the cold cathode fluorescent lamps (CCFLs) due to their high light-emitting efficiencies, high brightness and long lifespan.
A typical LED includes a substrate, a blue LED chip mounted on the substrate, and an encapsulant sealing the LED chip. The encapsulant is doped with yellow fluorescence. A light output surface is formed on a top portion of the encapsulant. During operation of the LED, the blue LED chip emits blue light. Part of the blue light is changed to yellow light by the yellow fluorescence. Other part of the blue light mixes with the yellow light, so as to generate white light. However, a distance between a center portion of the light output surface and the LED chip is less than that between an edge portion of the light output surface and the LED chip. Therefore, light transmitting from the LED chip to the edge portion of the light output surface has a longer optical path in the encapsulant than that of the light transmitting from the LED chip to the center portion of the light output surface. This causes yellow light halo to the LED, i.e. light radiating out from the edge portion of the output surface presenting a little yellow (warm white) and light radiating out from the center portion of the output surface presenting a little blue (cool white).
What is needed, therefore, is an LED which can overcome the limitations described.